Independant Rear Suspension

[thirdtimelucky 3]

James listen to these guys they are really clued up and there advice is priceless but if you want to do something different do it, it might out perform the others and unless you try you wont be satisfied. a well sorted torsion bar setup will out preform my 4wd. I only did it because people said it wouldn't work, I think I proved them wrong my original plan was to keep the rear beam and arb and fined some arms with the right camber and modify them to accept coilovers and brace them like the 206 gti180 and 206 sw but I couldnt get it to fit. ive designed some arms to suit my application but ran out of time to make them. a future project maybe. come over and see my setup on the lift I think its a bit heavy duty for a fwd car but it might give you some ideas.

 

Paul.

[Sandy 191]

Every race car i've ever seen uses an anti roll bar. I do a bit of mechanicing for a 306 racing in the Castle Combe Saloon championship. Last season it had no anti roll bars and it was putting in fairly average performances but this season it has both front and rear roll bars fitted and it's 2 seconds a lap quicker on tyres that are pretty hard now after being left outside all winter...and the track was pretty manky at the last meeting. Now to me that proves that ARB's are useful.

There's more to it than that Mark! Alan's car has been optimised to suit him on a particular circuit within a tight set of rules.

[aCe 0]

I dont question peoples expertease at all, i understand people have probably been down many different maybe similar routes before.

 

Ok so would it be better to:

 

Run a wide tracked beam with diffent arms and stiffer TB's - ARB

 

or

 

Mccpherson struts with 309 wishbones, custom hub assembly fixed to the wishbone to eliminate bump steer and rear srtuts?

 

The reason i'm keen on the strut idea is its adjustability, i'm not sure what would suit my style of driving (wether i need camber toe etc) @the back and therefore i would have to try loads of differents arms and setups of TB's to get the best =costing alot of money and time. The strut idea i was thinking is an easier option to exploit all of the possible geometry settings and adjust quickly.

 

I welcome input and feedback as i don't know what route to take, however the strut route is appealling heavily to me

[AdamP 0]

You started this thread with the aim of eliminating the lifting of the inside rear, however the likelihood is that the setup you're suggesting will still lift the inside rear when the car is balanced correctly as far as I can see. :-/

[Batfink 201]

I dont question peoples expertease at all, i understand people have probably been down many different maybe similar routes before.

 

Ok so would it be better to:

 

Run a wide tracked beam with diffent arms and stiffer TB's - ARB

 

or

 

Mccpherson struts with 309 wishbones, custom hub assembly fixed to the wishbone to eliminate bump steer and rear srtuts?

 

The reason i'm keen on the strut idea is its adjustability, i'm not sure what would suit my style of driving (wether i need camber toe etc) @the back and therefore i would have to try loads of differents arms and setups of TB's to get the best =costing alot of money and time. The strut idea i was thinking is an easier option to exploit all of the possible geometry settings and adjust quickly.

 

I welcome input and feedback as i don't know what route to take, however the strut route is appealling heavily to me

 

you wont get bump steer on the rear as you would fix the hub in position.

you will have the additional issue of having to work out suitable damper and spring rates.

[Rippthrough 98]

And the problem that you've shifted the effective roll centre massively, especially when cornering, as it'll migrate given you are proposing Mcpherson struts.

[aCe 0]

Rippthrough can you add to that?

 

Thanks for all the feedback its very interesting!

Edited May 13, 2009 by aCe

[DrSarty 90 1 Cars]

Rippthrough can you add to that?

 

Thanks for all the feedback its very interesting!

 

Agreed James. This is one of the most interesting threads for some time.

 

As it's covering suspension geometry from basic to advanced, I'll try and get a technical/practical explanation from Colin Satchell of what his set up involves, why it's used and how the car benefits. It may add to the info.

[aCe 0]

Yes that would be excellent

 

I'l await your reply

[gti_al 1]

There's more to it than that Mark! Alan's car has been optimised to suit him on a particular circuit within a tight set of rules.

 

After seeing you mention the cons of the front arb, i took mine for a spin when i had removed a droplink to diagnose a knocking noise. I think that single change was more dramatic than any other suspention modification i have tried in any 205, and a year later i still haven't reconnected it. I plan to do a few things to compensate for its removal, but even on stock suspention it feels nicer.

 

When i get the time, money and inclination i will change the springs/dampers to compensate for it not being there, but i think it is a very positive move. It felt a bit taily for a while, but now i'm used to it i wouldn't want to go back. The steering feel and traction on rough roads is a lot better

[Sandy 191]

Colin won't tell you exactly how he does it. But the basics are revised toe and camber, controlled droop, combined with vastly improved damping precision and matching spring rates.

[Batfink 201]

Agreed James. This is one of the most interesting threads for some time.

 

As it's covering suspension geometry from basic to advanced, I'll try and get a technical/practical explanation from Colin Satchell of what his set up involves, why it's used and how the car benefits. It may add to the info.

 

the rear is to get more damper control. The standard dampers move something like 1 inch to 4 inches of wheel movement.

With a turreted damper you can get 1:1 damping. Also with the coilover units you can alter spring rates and damper rates relatively simply as well as the ride height.

The front is widened to control weight transfer and ultimately create a car that can corner faster. He also does a few other adjustments to help bump steer and wishbone angle etc He also massively strengthens the subframe etc

 

Just with the rear setup (mine is similar by Mark Shillaber) it creates a very stable car over bumps and pretty much dials out the lift off oversteer.

As a trackcar is was fast and clinically smooth and I could keep up with trackday 205gti's despite having a 90bhp (fly) engine. I was able to ride the curbs quite well at coombe without the car balance getting upset and carry a lot of speed through the chicanes.

[kyepan 291]

"cocking a rear wheel is a charachteristic you will find with any good handling FF car" Reasons???????????

 

because there is a balance between linking the front and rear suspension with anti roll bars, and independantly allowing them to do their own thing.

 

if you want to kill roll, whack in a big bar to keep it flat, however whenever anything happens on one side, it will be transferred to the other via the roll bar, and your normal driving down bumpy roads will be interesting to say the least.

 

the ammount of roll needed to induce 3 wheel action is proportional to the spring rate in the opposite corner, and the force of cornering, roll center height, and center of gravity.

 

Lowering the roll center, putting weight lower down, and stiffening each corner will reduce this tendancy, but may not make you any faster, or the car easier to drive on the limit.

 

 

try not to grab hold of one dynamic factor, such as lifting a rear wheel, and let it rule your decisions on where to go with your suspension set up, if you really want to understand it, there are some really good books on the topic, and if i had time i would be reading them, as i don't understand how the dynamic factors (dynamic is my word of the day) affect each other in combination, hence the 'black art of suspension' mantra.

[Rippthrough 98]

Well, it'd take a while to go into because even roll centre calculations are a precise science as they don't directly influence behaviour how they were originally thought to, even the force-based kinematic roll centre models have flaws, but I really would recommend getting a few books on suspension kinematics.

 

Suffice it to say that roll-centres/fbrc's have a massive impact on the overall grip level, the weight transfer, stability, handling, etc, etc, they need to be carefully matched to ensure a grippy, good handling, benign car that doesn't try to kill you every time you head towards a corner, even worse, they need to match dynamically as the car moves through different attitudes - it's no good having a car that's balanced and grippy mid-corner if it tries to kill you on the way in and understeers like there's no tommorow on the way out.

So obviously, just bolting the front end strut setup in the back is going to play havoc with the handling - unfortunately this is what many used to do with the midengined Fiesta/Corsa/Escort conversions over the years, and suprise, surprise, they pretty much all handle like a bag of s*it and are almost lethal in the wet.

They get around it by making them very low and very stiffly sprung to reduce the effects of the weight shifting around, which is like putting a plaster on a broken leg.

 

There's a lot more to this than simply fabricating something that fits, there's a lot, lot more chance of getting it wrong than getting it right unless you sit down and do a lot of sums.

 

 

Right, now I've pissed on your bonfire...

Edited May 13, 2009 by Rippthrough

[aCe 0]

Lol no not at all it's interesting to hear peoples opinioons and the science hence this post.

 

So how would you reccomend a rear set up[?

[Rippthrough 98]

Either stick with trailing arms and turret the rear to improve the damping and reduce the rear kick up that trailing arms suffer from over bumps, or build a complete custom subframe with double wisbones at the rear, which is what me an' Ed are doing with our biege 1.1 beastie

Edited May 13, 2009 by Rippthrough

[aCe 0]

I see that rally novas run trailing arms with turreted rear struts. Whats is the advantages of this set up?

[thirdtimelucky 3]

Just a note on removing the front arb. The mot regs say that if one is fitted from manufacture it must be there for the mot. a lot of test stations miss this but make sure you dont remove the option to put the ard back for the mot. For clearance reasons I had to mount my arb under the subframe to get it through the mot.

 

Nice topic James, very interesting.

 

Paul.

[pug_ham 244 3 Cars]

I see that rally novas run trailing arms with turreted rear struts. Whats is the advantages of this set up?

Dont Nova's run rear shocks with the springs seperately mounted under the trailing arms?

 

It probably done for the 1;1 ratio as mentioned by Kev (Batfink)l;

the rear is to get more damper control. The standard dampers move something like 1 inch to 4 inches of wheel movement.

With a turreted damper you can get 1:1 damping. Also with the coilover units you can alter spring rates and damper rates relatively simply as well as the ride height.

 

I've been thinking about this a little more during today, I think its a big characteristic of a fast good handling fwd car.

 

Look at all the newest hot hatches of a similar size to the 205 & they all cock the inside rear wheel under hard cornering. (Clio, Megane, Fiat 500, Mini etc) & thats even with 25 years+ of chassis design advance so even though it is possible to work it out of the car, the end result just might not be as good as the original because of all the things you've had to upgrade to remove this trait.

 

I remember Daz_C saying after he followed me round Cadwell in February that my car likes to lift the inside rear wheel & thats running 20mm tb's with a 24mm rear arb, group N tarmac shocks & solid mounted beam with slightly lesser upgrades to the front of Koni top adjustables with 40mm lowering springs as supplied with the kit & group N top mount rubbers but its not a problem & it goes round the track very sweetly.

 

Graham.

[VisaGTi16v 1]

My Visa for those that don't know came out of the factory with the same front end as a 1.6 205 but the rear is from the earlier 104/Samba, ie independent trailing arms with 1:1 ratio coil overs and long ones at that and a ARB. Its very stable at the back and I can trail brake quite happily into bends. No way I could do the same in others ive owned like the zx/xsara or 205, it was almost ridiculous how easily the back would step out on the 205 I owned!

 

It does still lift the inside wheel though sometimes but then it has been lowered a bit Pic

 

Its also worth noting that the back of the Visa is 4" or so narrower than the front, it almost looks ridiculous when following, like its crabbing. I don't claim to be an expert but ive read enough from the people who do know what they are doing and sorting the rear out is as important if not more than the front, putting on a wider 309 beam helps but its not solving the problem at heart, just making it less visible...

[Cameron 16]

There's nothing wrong with trying something new, just as long as you do it properly. As people have said, simply sticking the front suspension setup into the back won't really help, and I think the idea of keeping the trailing arms on a new subframe is also flawed.

If you're going to do it, you need to make a proper job of it, which means you need to get your head into some books and learn a hell of a lot of complicated maths. Then you need to design the thing so it won't be weak or unnecessarily overbuilt, i.e FEA testing. I'm planning on making this my final year project (that is if I don't end up doing formula student) as I think there are huge gains to be made with a properly independent rear setup. But it isn't really cocking a wheel that's my motivation, its being able to have decent geometry under cornering without having an absurd amount of static camber!

[Batfink 201]

My Visa for those that don't know came out of the factory with the same front end as a 1.6 205 but the rear is from the earlier 104/Samba, ie independent trailing arms with 1:1 ratio coil overs and long ones at that and a ARB. Its very stable at the back and I can trail brake quite happily into bends. No way I could do the same in others ive owned like the zx/xsara or 205, it was almost ridiculous how easily the back would step out on the 205 I owned!

 

It does still lift the inside wheel though sometimes but then it has been lowered a bit Pic

 

Its also worth noting that the back of the Visa is 4" or so narrower than the front, it almost looks ridiculous when following, like its crabbing. I don't claim to be an expert but ive read enough from the people who do know what they are doing and sorting the rear out is as important if not more than the front, putting on a wider 309 beam helps but its not solving the problem at heart, just making it less visible...

 

the 309 rear beam will make the rear more stable. Sandy always told me that the front width should be widened rather than the rear. I'm sure a search can bring up what he said....

I'm running a 309 rear beam but at the same time increasing the front beyond the 309 front track width.

 

 

There's nothing wrong with trying something new, just as long as you do it properly. As people have said, simply sticking the front suspension setup into the back won't really help, and I think the idea of keeping the trailing arms on a new subframe is also flawed.

If you're going to do it, you need to make a proper job of it, which means you need to get your head into some books and learn a hell of a lot of complicated maths. Then you need to design the thing so it won't be weak or unnecessarily overbuilt, i.e FEA testing. I'm planning on making this my final year project (that is if I don't end up doing formula student) as I think there are huge gains to be made with a properly independent rear setup. But it isn't really cocking a wheel that's my motivation, its being able to have decent geometry under cornering without having an absurd amount of static camber!

 

Hi Cameron. I have a rough design in my head on how I want a lightweight rear trailing arm setup. Fancy building that as a comparison to your setup

 

Kev

[VisaGTi16v 1]

Batfink: thats pretty much what I said heh

[Batfink 201]

ok

I want a picture of your car looking like its crabbing

[Rippthrough 98]

Hi Cameron. I have a rough design in my head on how I want a lightweight rear trailing arm setup. Fancy building that as a comparison to your setup

 

Kev

 

I'll do it you

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bring one of those signed blank cheque thingies.